Conventional computer displays, such as cathode ray tube (CRT) displays, liquid crystal displays, electroluminescent displays, and the like present a light output representing characteristics of an image. The image may be a graphical or pictorial one, an artistic one without any particular form, an alphanumeric one (including various alphabets and/or number systems), etc. Usually the image is presented on a screen which may be flat or somewhat curved, it being appreciated that substantial effort currently is being expended in providing developments for improvements in flat displays, such as those known as flat panel displays.
Usually such conventional displays must be sufficiently large to permit the displayed image, whether graphical, alphanumeric, or other, to be viewed comfortably by a person. Exemplary displays used on portable computers usually have a diagonal dimension exceeding nine inches. Some personal organizer type computers, such as those known as a personal digital assistant, have smaller displays, but in any event the display must be sufficiently large to be read by a person. Usually the larger the display, the greater the cost. Also, the larger the display, the greater the weight.
Over the years substantial effort has been applied to expand the viewing angle for many displays, for example, off-axis viewing can be enhanced in a liquid crystal display by using optical retarders, as is disclosed in U.S. Pat. No. 4,385,806. A disadvantage when a display has a wide field of view is the lack of privacy; for example, as an individual is working on a portable computer while riding on a public vehicle, another rider may too easily observe the display. Another disadvantage is the wide distribution of light output that may occur when there is a wide angle of view provided by a display; such wide distribution may reduce the brightness, intensity and/or contrast of the display.
An effort is made herein to distinguish between field of view and angle of view (also referred to sometimes as viewing angle). A field of vie usually refers to how wide an image looks or appears to the eye or how much of a display is able to be seen at one time. The angle of view is usually refers to the angle at which one looks at or can look at an image, display, etc. For example, a narrow angle of view at which a monitor (or some other display device) must be viewed means that although the full monitor can be viewed, such viewing can be had from only a relatively small spot, or even from one spot or position. However, that monitor may present a relatively wide field of view to the viewer. As another example, in a heads up speedometer display of an automobile, the angle of view usually is relatively narrow so only the driver sees the display,; but the field of view usually is sufficiently wide to permit all of the desired information to be seen by the driver.
One prior approach to provide privacy in viewing a display has been to use a head mounted display which is supported on the head of a user (or on some other body part, for example), a helmet mounted display, etc. and provides a closed area in which the eye(s) view(s) the images provided by the display. Such displays sometimes provide increased immersion into the image whereby the user can observe the displayed images without being distracted by other visual stimuli, etc. Another technique for increasing the private viewing of a display has been to use a binocular, telescope or microscope type system through which the observer looks to see an image.
It is desirable that a display have adequate eye relief and comfort with which images can be viewed. One aspect of comfort is the distance at which the image is viewed or appears to be located relative to a viewer's eye(s); a comfortable viewing distance is about 20 inches or more, for example, approximate reading distance. This distance physically can be changed using lenses, e.g., eyeglasses, but the apparent distance of the image should be maintained at a comfortable distance, for example, twenty inches or more. An aspect of eye relief is the distance between the eye and the last optical element closest to the eye, such as the output objective of a microscope, telescope, etc. Often, it is desirable that such distance be relatively large to provide adequate eye relief. Without adequate eye relief and/or comfortable viewing distance, a person's eye(s) may be strained to view an image and/or otherwise caused discomfort.
A problem with many prior display systems is the relatively large amount of power required to operate the display. For example, a power hungry display is especially disadvantageous in a battery powered computer, in a video display used in a vehicle, such as an automobile, aircraft, watercraft, etc., where there may be a limited supply of power. It also would be desirable to reduce the power required for a display and/or the power requirements of a device, such as a computer, video display system, etc., which uses a display.
Removal or reduction of glare in or on a display is another problem for which substantial effort has been expended in the past. Glare usually is due to the reflection of ambient light from a display screen, monitor, liquid crystal display, cathode ray tube, electroluminescent display, etc. Most efforts in the past to try to reduce glare also have reduced the brightness of the image presented by the display. It would be desirable to reduce glare while minimizing the impact on the brightness of the image presented by a display. At technique for glare reduction is disclosed in the concurrently filed patent application and can be used in the instant invention, too
Several other features and advantages of the present invention are summarized here. These features and advantages may be used alone and/or in combination with other features, aspects and/or advantages described herein. For example, the invention may be used to provide an enlarged and relatively private view over a relatively narrow angle of view of a relatively small display, image source, etc., while providing a relatively wide field of view. Light may be collected so that a relatively large amount is directed to the retina of a viewing eye while reducing the amount of light which is otherwise lost to the system, thus enabling the display to be relatively bright without requiring an especially bright source of light for the display, image source, etc. Also, since the viewing system may be used to enlarge the image provided by the source, a relatively small source can be used to supply the image for viewing. The smaller source can reduce power requirements, weight, etc., as is known. The light may be spread over the retina of the viewing eye and, therefore, the space between pixels (picture elements) of the image source, such as a liquid crystal display, for example, tends to be somewhat dampened thereby to reduce the distinction seen between pixels and optically inactive space in the display. Further, using the glare reducing technique hereof, glare can be reduced without significantly reducing brightness of the viewed output.
With the foregoing in mind, then, there is a need to provide the ability to view in private an image provided by a source such that the viewed image is enlarged relative to the size of the image at the source.